How Do Death Valley’s “Sailing Stones” Move Themselves Across the Desert?- page 2 | Travel | Smithsonian
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How Do Death Valley’s “Sailing Stones” Move Themselves Across the Desert?

These mysterious rocks have puzzled scientists for decades—until one geologist found the answer on his kitchen table

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As the research team studied weather patterns on the Racetrack, they also looked for rocks that seemed to move on their own in other environments. Scanning the scientific literature, Lorenz learned that the buoyancy of ice helped float boulders onto arctic tidal beaches, creating barricades along the shore. The scientists began putting this idea together with what they saw on the Racetrack. “We saw one instance where there was a rock trail and it looked like it hit another rock and bounced, but the trail didn't go all the way up to the other rock, like it was repelled somehow,” says Lorenz. “We thought if there was a collar of ice around the rock, then it might be easy to imagine why it might bounce.”

Eventually, Lorenz employed a tried-and-true method for testing his nascent idea: the kitchen-table experiment. “I took a small rock, and put it in a piece of Tupperware, and filled it with water so there was an inch of water with a bit of the rock sticking out,” he says. “I put it in the freezer, and that then gave me a slab of ice with a rock sticking out of it.” He flipped the rock-ice hybrid upside down and floated it in a tray of water with sand on the bottom. By merely blowing gently on the ice, he realized, he could send the embedded rock gliding across the tray, scraping a trail in the sand as it moved. After decades of theoretical calculations by countless scientists, the answer seemed to be sitting on his tabletop.

Lorenz and his team presented their new model in a 2011 paper. “Basically, a slab of ice forms around a rock, and the liquid level changes so that the rock gets floated out of the mud,” he explains. “It’s a small floating ice sheet which happens to have a keel facing down that can dig a trail in the soft mud.” Calculations show that, in this scenario, the ice causes virtually no friction on the water, so the stones are able to glide with just a slight breeze. The team argues that their model accounts for the movement far better than any other, since it doesn’t require massive wind speeds or enormous ice sheets.

Still, says Ranger Van Valkenburg, most visitors to the Racetrack seem to resist this concrete explanation for such a peculiar phenomenon. “People always ask, ‘what do you think causes them to move?’ But if you try to explain, they don't always want to hear the answers,” he says. “People like a mystery—they like an unanswered question.”

In a way, though, Lorenz’ physical explanation really need not diminish the feeling of awe the sailing stones bring about—it can heighten it. You can get a sense of it by sitting at the playa and imagining the perpetual sailing of the stones over time, stretching into millennia. As human societies rise and fall, and as cities are constructed and then left to disintegrate, the stones will glide gradually around their playa, turning back and forth. Frozen in ice and nudged by the slightest of breezes, they will endlessly carve mysterious, zigzagging paths into the hard flat ground.

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